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Exhaust air heat recovery system evaluation for multiple make flue-cured tobacco bulk barns

MACIALEK J.A.; ELLINGTON G.H.

North Carolina State University, Raleigh NC USA

Fuel savings from an exhaust air heat recovery system installed in bulk curing barns were evaluated at on-farm locations in Wilson, Sampson, Vance, Edgecombe, Pamlico counties in North Carolina and Rawlings, Virginia this past season. The heat recovery system consists of a heat exchanger (recovery coil) mounted in the exhaust air vent and an additional heat exchanger (preheat coil) mounted in the fresh air intake vent. A fractional horsepower (1/20) pump circulates water continuously between the two heat exchangers in a closed-loop system during curing. The warm exhaust air passes through the recovery coil and heats the water that is pumped to the preheat coil where the thermal energy recovered is transferred to the incoming ambient air stream. The water exists the preheat coil and returns to the recovery coil and the cycle is repeated. The system is able to preheat the ambient air temperature 30oF to 40oF during peak performance. At each location, a direct fuel comparison was evaluated between two identical make barns. The fuel savings averaged over the 2017 season for the six locations ranged from less than one percent to 13 percent per cure. This was an average savings of 1.5 gallons to 44 gallons of LP gas per cure. Average burner operating times were reduced approximately 13 to 15 hours per cure. Energy recovered ranged from 1,000 to 30,000 Btu/hour. Grower feedback from all locations indicated there were no differences in the cured leaf quality between the barns. Additionally, the cure duration was not extended when comparing a barn with the system and a barn without. (Reprinted with permission)